What to Consider When Buying a Home Battery

You have a solar system at home because you want to reduce your electricity bill, and do your part for the environment. Now you want to take it to the next step and you’re considering buying a battery – but you’re not too sure what to look for. Buying a battery can be an intricate task since there are multiple factors to consider.

Battery Type

When looking for which type of batteries to buy, there are a couple of alternatives currently on the market. Each have their own advantages and disadvantages, so look for ones that suit your priorities and needs.

Lead

Lead batteries have been in the market for a long time, so we have a reliable knowledge of its strength and weakness. These batteries are good as an ‘entry-level’ option because they have low up-front costs, and widely available in the market – as long as the buyer are aware of its capabilities.

There are 3 types of lead batteries you should look out for: flooded/wet, absorbent glass mat (AGM) and gel. Flooded batteries run within a solution that will generally require maintenance, while the other two are more or less maintenance free. Flooded is also cheapest up-front.

Lead batteries, although wide in variety, share a common downfall. They are intolerant to deep cycles and fast discharges – meaning you can’t drain the battery like you can with a phone then recharge it to full capacity again nor can you draw out a large amount of electricity in a short amount of time. Consequently, you must treat lead batteries relatively gently as doing either of these things will significantly compromise the lifetime and efficiency of the battery.

The production of lead batteries causes environmental damage, but due to their widespread application, there are many recycling options when the battery reaches the end of its lifetime of 5 to 15 years

Pros:

Cheap

Reliable

Cons:

Need maintenance

Not good for deep cycling – dual purpose or as backup power

5-15 years lifetime

Bulky (low energy density)

Lithium

Lithium based batteries has emerged more recently in the market and is the main competitor towards traditional lead batteries –with good reason. These batteries have a higher up-front cost (in the current market), but have key advantages and is good for those who want to seriously invest in a battery system for their solar and reduce their reliance on the grid.

Lithium batteries are compact, and can be placed in more discrete locations and is also maintenance free. They are also robust and tolerant to deep and fast discharges – so you can utilise most of the storage capacity of the battery, as well as drawing electricity quickly.

One main concern with lithium batteries relates to its innate combustibility. Internal components must be kept separate, because they can react violently with the air to generate heat and produce fire. Manufacturers overcome this with stringent production methods and safer designs.

Pros:

Reliable

Maintenance free

Tolerant to fast charge/discharge

Compact

Cons:

Combustible

Expensive

Other types of batteries

There are other battery chemistry alternatives. Rarely seen is nickel chloride batteries, whose main advantage is its robustness and its recyclability, but at a higher upfront cost. Other new battery technologies have emerged in recent years, including ‘flow’ batteries and saltwater based batteries, each with its owns advantages.

Key specification

Storage capacity and depth of discharge

To find the appropriately size system, you should know the storage capacity of the battery. But be mindful. Batteries have a total capacity (nominal) and a ‘usable’ capacity. This is because batteries can’t discharge their full capacity without damaging itself. To put in perspective, smartphones may have 16 gigabytes of storage capacity, but only 12 gigabytes is usable because the rest is for crucial software, without which the phone can’t run.

Power output

This refers to the rate of electricity the battery can provide (in kW). In essence, a higher value means more electricity can be provided in a given time. There are two parts to output: continuous and peak. Continuous is the rate of electricity the battery can provide, and maximum is the rate the battery can reach for a short period (matter of seconds) during a large demand spike.

For example, your electricity demand will spike if you turn on multiple appliances at the same time. This is important if you are considering going off-grid, because there is no backup power source to meet the demands in your home.

Storage (round-trip) efficiency

Battery storage, like many things in life, is not perfect. You will not get the same amount of electricity out, compared to what you put in. For example, a 10kWh battery with 85% efficiency will let you draw a maximum of 8.5 kWh.

Cycle life and warrantied energy throughput

Knowing how long your battery will last is crucial. The duration of a battery’s working life can be measured in charge cycles or warrantied energy throughput, which is arguably more important.

Batteries will need to be replaced after being charged/discharged a certain number of times. Normally, you will not go through more than one cycle per day if you charge your battery with your solar panel. This means that a battery with a cycle life of 3650 cycles will last 10 years.

However, as batteries lose efficiencies over time, a ‘full charge’ can be at 100% of its claimed capacity at the start, but dwindles to 70% after some years. This is why warrantied energy throughput is more useful to determining how long your battery can last. This number shows the amount of electricity to pass through the battery throughout its lifetime.

With this knowledge, you should now be well equipped to buying the right battery for your home. If you want to make the most out of your solar and battery investment, consider getting an energy management system like carbonTRACK, which not only shows the data related to electricity usage, input and output, but can also control appliances in home so that you can maximise your savings from electricity use.